Decoherence of Bell states by local interactions with a suddenly quenched spin environment

作者：Wendenbaum Pierre; Taketani Bruno G; Karevski Dragi^*

来源：Physical Review A, 2014, 90(2): 022125.

DOI：10.1103/PhysRevA.90.022125

We study the dynamics of disentanglement of two qubits initially prepared in a Bell state and coupled at different sites to an Ising spin chain in a transverse field (ITF) playing the role of a dynamic spin environment. The initial state of the whole system is prepared in a tensor product state rho(Bell) circle times rho(chain), where the state of the chain is taken to be given by the ground state vertical bar G(lambda(i))%26gt; of the ITF Hamiltonian H-E(lambda(i)) with an initial field lambda(i). At time t = 0(+), the strength of the transverse field is suddenly quenched to a new value, lambda(f), and the whole system (chain + qubits) undergoes a unitary dynamics generated by the total Hamiltonian H-Tot = H-E(lambda(f)) + H-I, where H-I describes a local interaction between the qubits and the spin chain. The resulting dynamics leads to a disentanglement of the qubits, which is described through Wootters%26apos; concurrence, due to their interaction with the nonequilibrium environment. The concurrence is related to the Loschmidt echo, which in turn is expressed in terms of the time-dependent covariance matrix associated with the ITF. This permits a precise numerical and analytical analysis of the disentanglement dynamics of the qubits as a function of their distance, bath properties, and quench amplitude. In particular, we emphasize the special role played by a critical initial environment.

• 出版日期2014-8-29